The invention relates to an apparatus for guiding a wire or strip-like cutting electrode on a machine tool and, particularly an apparatus for controlling the axial tension of a wire or strip-like tool electrode in the working zone.
In conventional spark-erosive or electrochemical cutting installations, a desired contour is cut in a workpiece with the aid of wire or strip electrodes. The wire or strip electrode generally comprises a wire with a diameter between 0.01 and 1.00 mm or, in special cases, strips of a corresponding cross-section. Spark-erosive machining, as a result of an electronic process control, permits a very high machining accuracy, which is typically approximately 0.001 mm. Thus, very high precision demands are made on the guidance and driving means for the wire electrode.
An important part in the maintaining of the desired machining precision is played in such installations by devices for driving and guiding the cutting wire. For example, wire guide means for spark-erosive or electroerosive cutting are known from West German Pat. No. 26 25 349. A loop of the of the cutting wire is completely disengaged from the supply and take-up side of the machine and is driven in the working zone by means of fixed speed driven roller pairs. The wire in the working loop is them tensioned by special means, e.g. weights or springs, and is guided in very precise guide rollers. These means have proved satisfactory in practice.
With the increased use of spark-erosive cutting in conjunction with special electronic controls which control the relative position between two wire guide heads bounding the working zone, as described in West German Pat. No. 20 52 261, it has also known in the case of large wire slope angles to correspondingly orient the wire guide heads, as is known from Patent Application No. WO 80-02395.
If the guide heads are relatively strongly pivoted or oriented in operation on spark-erosive cutting equipment equipped with the described wire drive, the wire drive housed in the yoke of the equipment must exert very high forces on the guide heads, due to the relatively high wire tension, e.g. 500 to 2500 g, in the working loop of the wire electrode. The mounting supports and drive means, as well as the brackets for the oriented wire guide heads, can therefore be appreciably deformed and deflected. This is particularly the case when it is necessary to work with a relatively large wire angle, that is, with a strong lateral relative displacement of one of the guide heads with respect to the other. As the wire guide heads are directly responsible for determining the geometry of the workpieces and the cutting precision, such deformations are undesirable for very precise machining tasks. Further, the placement of the complete wire drive and guide means directly on the oriented guide heads is not technically advantageous due to the bulk of the construction.